In the field of graphic art, printing plates are printed by use of a set of color separation films prepared from a color original by use of lith films. In general, in order to check errors in the color separation process or necessity of the color correction before printing (practical printing operation), a color proof is prepared from color separation films. To the color proof, realization of high resolving power that enables high reproduction of medium images and performance such as high stability to the process are expected. Furthermore, in order to obtain the color proof similar to practical printed matter, materials practically used for printed matter are preferably used as materials for the color proof, for example, actual printing paper (regular paper used in running on to give a final product) is used as a base and pigments are used as coloring materials. Moreover, for the preparation of the color proof, a dry process where no developing solution is used has been highly desired.
With contribution of an electronic system in the latest pre-process of printing (prepress field), a recording system for preparing directly the color proof from digital signals has been developed as the dry process for preparing the color proof. This electronic system aims at preparing the color proof of a particularly high image quality. In general, a dot image of 150 lines/inch or more are reproduced. In order to record the proof of a high image quality from the digital signals, the laser beam that can be modulated by digital signs and can be stopped down as recording beams are used as recording heads. Recording materials having high recording sensitivity to the laser beam and high resolving power that enables reproduction of highly fine halftone dots must be developed.
Known recording materials used for a method for forming a transfer image by making use of the laser beam are hot melt transfer sheets having a light-to-heat conversion layer that absorbs the laser beam to generate heat and an image-forming layer that contains pigment dispersed in components such as a hot melt wax and a hot melt binder on a support in this order (Japanese Patent Laid-Open No. 58045/1993). In the method for forming images by using these recording materials, heat generated in areas irradiated with the laser beam in the light-to-heat conversion layer melts the image-forming layer corresponding to the areas, and the melted areas transfer to an image-receiving sheet laminated on a transfer sheet to form a transfer image on the image-receiving sheet.
Furthermore, Japanese Patent Laid-Open No. 219052/1994 discloses a thermal transfer sheet where a light-to-heat conversion layer containing a light-to-heat convertible substance, a heat peel layer formed of a very thin film (0.03 to 0.3 μm), and an image-forming layer containing a coloring material are provided on a support in this order. In this thermal transfer sheet, binding power between the image-forming layer and the light-to-heat conversion layer that are bound through the aforesaid heat peel layer reduces by irradiation with the laser beam to form a highly fine image on an image-receiving sheet laminated on the thermal transfer sheet. In this method for forming images by use of the thermal transfer sheet, the so-called “abrasion” is utilized. This phenomenon is utilized as follows: In areas irradiated with a laser beam, the heat peel layer is partly decomposed and vaporized, the binding power between the image-forming layer and the light-to-heat conversion layer in the areas is weakened, and the image-forming layer in the areas is transferred to the image-receiving sheet laminated thereon.
These methods for forming images have the advantages in that the actual printing paper having an image-receiving layer (adhesive layer) attached can be used and the multicolor image is obtained with ease by transferring successively images different in color to the image-receiving sheet. These methods enable easy formation of highly fine images and are useful for the preparation of the color proof (DDCP: direct digital color proof) or a highly fine mask image.